# std::is_volatile

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< cpp‎ | types

Defined in header `<type_traits>` |  |
template< class T > struct is_volatile; |  | (since C++11)

`std::is_volatile` is a UnaryTypeTrait.

If `T` is a volatile-qualified type (that is, volatile, or const volatile), provides the member constant value equal to true. For any other type, value is false.

If the program adds specializations for `std::is_volatile` or `std::is_volatile_v`, the behavior is undefined.

### Template parameters

T | - | a type to check

### Helper variable template

template< class T > constexpr bool is_volatile_v = is_volatile<T>::value; |  | (since C++17)

## Inherited from std::integral_constant

### Member constants

value [static] | true if `T` is a volatile-qualified type, false otherwise (public static member constant)

### Member functions

operator bool | converts the object to bool, returns value (public member function)
operator() (C++14) | returns value (public member function)

### Member types

Type | Definition
`value_type` | bool
`type` | std::integral_constant<bool, value>

### Possible implementation

    template<class T> struct is_volatile : std::false_type {};
    template<class T> struct is_volatile<volatile T> : std::true_type {};

### Example

Run this code

    #include <type_traits>
    #include <valarray>

    static_assert(!std::is_volatile_v<int>);
    static_assert(std::is_volatile_v<volatile int>);
    static_assert(std::is_volatile_v<volatile const int>);
    static_assert(std::is_volatile_v<volatile std::valarray<float>>);
    static_assert(!std::is_volatile_v<std::valarray<volatile float>>);

    int main() {}

### See also

is_const (C++11) | checks if a type is const-qualified (class template)

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